Seapower Platform Surviving Storms

The Seapower Platform – 1:5 Scale Galway Bay Project

A small Irish engineering company Sea Power Ltd. launched their 1:5 scale Wave Energy Converter (WEC) test platform in open water sea trials in Galway Bay kindly funded and supported by SEAI, Ireland.

In parallel with this is an intensive Cost Of Energy reduction programme funded by WES.

The platform itself has had an Irish patent granted for some time, but has now been recently patented internationally. The WEC has gone through many rigorous levels of numerical analyses and small scale tank testing. It is designed to harness the energy in deep water waves, and the company is committed to achieving this at the lowest LCOE possible, making it more competitive than other renewable, and non-renewable, energy sources. The recent experience at the open water test site and the work ongoing under WES programmes have given the engineers great encouragement to pursue this technology so that it will be ready for the energy market in the 2020s.

The Seapower Platform is a stable, hinged platform that is ideal for development of on-board power take off systems, and for accessibility during testing. It is long machine with a low visual profile and further optimisation work will lead to machines with even lower visual profile. Pontoon size optimisation is due in later stages to optimise the pontoon draughts, add curved features where hydrodynamically appropriate, all aimed to further lower CapEx levels.

The medium scale (1:5) Seapower Platform was towed from Foynes Port in Limerick where it was constructed last year, to Galway Harbour where a Cork-based marine operations company Atlantic Towage Ltd. hooked up with and installed the WEC and her mooring system into the Smartbay test site. This operation took place at the end of October 2016 and the WEC has been operating successfully on site since then, surviving multiple storms on the site. The operation also demonstrated a winter deployment and his accomplished most of its objectives for Phase 1.

Demonstrate that the production of utility-compliant electricity or production of desalinated freshwater for a sustained period is possible -based on average mechanical power measurements.

Verification of the power curve of this device against the measured power curve from prior model scale tank tests.

Creation and publication of the platform’s power matrix to IEC standards.

Confirmation of the feasibility of the deployment, operation and recovery of the Seapower Platform

Recording of the environmental interactions of the Project in order to demonstrate and verify that it has minimal impact on the Smartbay site

For Phase 1 of the 1:5 scale project, power is measured directly by common mechanical means – i.e. an on-board rectilinear dynamometer. The mechanical power is measured across a wide range of sea states which enables the power curve to be plotted. In the safe and small scale environment of the wave tank, these mean wave periods typically range between 1 and 2 seconds. For the medium scale device deployed at Galway bay, these correspond to a range between 2.25 seconds and 4.5 secondsfor Galway Bay, and for full scale systems these correspond to approximately 5 and 10 second mean periods which typically occur off the coast of Mayo. Currently this 1:5 scale WEC is built from cuboid steel pontoons which are supported by steel beams or steel lattice chassis structure.

Sea Power Ltd. are involved in a material study with ARUP and Cruz Atcheson to determine if there is any economic advantage in using novel concrete based materials.

Since the launch date, the WEC has already demonstrated survival in extreme conditions. For this 1:5 scale of device, it has already survived maximum instantaneous wave heights of 4.1 metres (Hs=2.05m at the test site). For an equivalent full scale Seapower Platform, this is survival inHs=10.25metres conditions – or approximately 20.5m instantaneous wave height. Wave conditions are monitored and then recorded to Seapower’s SCADA system from the Marine Institutes’ digital ocean portal, and accurate sea state predictions are also available which has proved to be invaluable.

Relative angular motion and high torque is developed around the hinge and the machine tends to pitch and heave in this degree of freedom in a wide range of sea states. This hinge on the WEC suits the integration of a rotary PTO which is under development with a number of Sea power’s partners including Limerick Wave Ltd. and Romax Technologies. This realistic PTO will be the subject of works for Phase 2 of the 1:5 scale project. The WEC has a good power curve that has been established by third party in tank testing environments.

The Seapower Platforms can be easily towed, hooked up to mooring systems, or transported back to harbours or small piers. Seapower hope to remain testing at the site for a 12 month continous period with the installation of the rotary PTO mid way in between the deployment duration.

Throughout the testing period in Galway Bay, a number of onboard parameters are being continuously measured. These are: tension loads in the front mooring lines, bow panel pressures due to wave slapping and wave slamming events, multiaxis hinge load in both hinge pins, accelerations of each body, and mechanical power in the representative PTO system. The WEC also has a number of condition monitoring systems in place – including temperature monitoring of the control system and brake, water ingress sensors, and GPS location monitor. The engineers at Seapower also monitor their device using a remote camera located on the mast. So far, all mechanical, electrical and ontrol systems are performing exactly as expected and the data is streaming from the onboard DAQ at a very high rate. Post processing of this data is ongoing and the Marine Intitute and MaREI are also assisting in this regard.

The onboard parameters being measured, directly inform future structural and mechanical design calculations for optimised full scale platforms. For example, mooring loads in survival conditions at the medium scale can be scaled up to full scale loads. These loads are the main driver for cost. This means that design loads at full scale determine the size of mooring components and hence determine the capital cost involved. Once these costs are established, they are inputted into a detailed LCOE calculation to determine the feasibility of the platform as a method of converting ocean energy.

Marine activities on the Galway Bay site are supported in a practical way with the help of staff at Smartbay and the Marine Institute in Galway and SEAI. SmartBay offers multidisciplinary expertise to wave energy developers and Sea Power Ltd have benefited tremendously from this. The Smartbay site is pre-fitted with weather, wave measuring equipment, sub-sea data and power cables and a dedicated radio telemetry which facilitates data capture back to shore.

The Seapower Platform has demonstrated survival during storms Barbara and Doris, and we expect it to survive for the rest of the deployment period.